Generally, a hydraulic excavator as a representative example of a construction machine is constituted by an automotive lower traveling structure, an upper revolving structure swingably mounted on the lower traveling structure, and a working mechanism liftably mounted on the front side of the upper revolving structure.
The upper revolving structure is provided with a revolving frame serving as a support structural member, an engine mounted at the rear side of the revolving frame, and a cab located at the left front side of the revolving frame to be positioned along the left side of the working mechanism.
An operator's seat is provided on a floor member as a bottom surface in the cab, and an indoor unit of an air conditioner is arranged in rear of the operator's seat. A cab box constituting a contour of the cab is provided with an inspection cover positioned on a left surface of the cab box where an operator gets on and off, wherein the inspection cover covers a filter for purifying external air aspired by the indoor unit to be capable of opening and closing (for example, Patent Document 1: Japanese Patent Laid-Open No. 2006-57245 A).
On the other hand, a diesel engine is adopted as the engine in the hydraulic excavator, and the diesel engine is supposed to discharge a large amount of nitrogen oxides (hereinafter, referred to as NOx) and the like. Therefore, a NOx purifying device for purifying NOx is known as a post-treatment device of the exhaust gas in the diesel engine. The NOx purifying device is provided in an exhaust pipe of the engine and, for example, is largely constituted by a urea selective reduction catalyst for removing NOx in the exhaust gas, a urea water tank for reserving a urea solution as a reducing agent, a urea water injection valve for injecting the urea solution in the urea water tank toward the upstream side of the urea selective reduction catalyst, and a connecting pipe connecting the urea water tank and the urea water injection valve.
The urea water to be reserved in the urea water tank is preferably arranged in a temperature environment of, for example, the range of a temperature of 4° C. to 60° C. for preventing freeze and crystallization of the urea water. Therefore, the urea water tank is arranged near an engine, a hydraulic pump, a control valve, a hydraulic motor, an operating oil tank, or the like as a heat source generating heat by an operation thereof. On the other hand, a space in which the temperature environment is stable in the hydraulic excavator is an inside of the cab as a living space of the operator, and therefore the urea water tank is arranged in the cab. (for example, Patent Document 2: Japanese Patent Laid-Open No. 2003-20936 A).